From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, HK_RANDOM_FROM,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id ACFA2FA372A for ; Wed, 16 Oct 2019 16:25:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8C8C62168B for ; Wed, 16 Oct 2019 16:25:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2406275AbfJPQZe (ORCPT ); Wed, 16 Oct 2019 12:25:34 -0400 Received: from mga17.intel.com ([192.55.52.151]:53038 "EHLO mga17.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2392349AbfJPQZe (ORCPT ); Wed, 16 Oct 2019 12:25:34 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga107.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 16 Oct 2019 09:25:33 -0700 X-IronPort-AV: E=Sophos;i="5.67,304,1566889200"; d="scan'208";a="189729232" Received: from xiaoyaol-mobl.ccr.corp.intel.com (HELO [10.255.31.58]) ([10.255.31.58]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/AES256-SHA; 16 Oct 2019 09:25:29 -0700 Subject: Re: [PATCH v9 09/17] x86/split_lock: Handle #AC exception for split lock To: Paolo Bonzini , Thomas Gleixner Cc: Sean Christopherson , Fenghua Yu , Ingo Molnar , Borislav Petkov , H Peter Anvin , Peter Zijlstra , Andrew Morton , Dave Hansen , Radim Krcmar , Ashok Raj , Tony Luck , Dan Williams , Sai Praneeth Prakhya , Ravi V Shankar , linux-kernel , x86 , kvm@vger.kernel.org References: <1560897679-228028-1-git-send-email-fenghua.yu@intel.com> <1560897679-228028-10-git-send-email-fenghua.yu@intel.com> <20190626203637.GC245468@romley-ivt3.sc.intel.com> <20190925180931.GG31852@linux.intel.com> <3ec328dc-2763-9da5-28d6-e28970262c58@redhat.com> <57f40083-9063-5d41-f06d-fa1ae4c78ec6@redhat.com> <8808c9ac-0906-5eec-a31f-27cbec778f9c@intel.com> From: Xiaoyao Li Message-ID: Date: Thu, 17 Oct 2019 00:25:27 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/16/2019 11:37 PM, Paolo Bonzini wrote: > On 16/10/19 16:43, Thomas Gleixner wrote: >> >> N | #AC | #AC enabled | SMT | Ctrl | Guest | Action >> R | available | on host | | exposed | #AC | >> --|-----------|-------------|-----|---------|-------|--------------------- >> | | | | | | >> 0 | N | x | x | N | x | None >> | | | | | | >> 1 | Y | N | x | N | x | None > > So far so good. > >> 2 | Y | Y | x | Y | Y | Forward to guest >> >> 3 | Y | Y | N | Y | N | A) Store in vCPU and >> | | | | | | toggle on VMENTER/EXIT >> | | | | | | >> | | | | | | B) SIGBUS or KVM exit code > > (2) is problematic for the SMT=y case, because of what happens when #AC > is disabled on the host---safe guests can start to be susceptible to > DoS. > > For (3), which is the SMT=n case,, the behavior is the same independent of > guest #AC. > > So I would change these two lines to: > > 2 | Y | Y | Y | N | x | On first guest #AC, > | | | | | | disable globally on host. > | | | | | | > 3 | Y | Y | N | Y | x | Switch MSR_TEST_CTRL on > | | | | | | enter/exit, plus: > | | | | | | A) #AC forwarded to guest. > | | | | | | B) SIGBUS or KVM exit code > I just want to get confirmed that in (3), we should split into 2 case: a) if host has it enabled, still apply the constraint that guest is forcibly enabled? so we don't switch MSR_TEST_CTL. b) if host has it disabled, we can switch MSR_TEST_CTL on enter/exit.